1. Field of the Invention
The invention relates generally to fuel burning heaters, more particularly, relates to a fuel burning heater having an inline heater for heating fuel that is bound for the burner. The invention additionally relates to a method of operating such a machine.
2. Discussion of the Related Art
Performing construction work in cold weather climates faces many challenges that are not confronted in warmer climates. In the context of excavation and earth-moving, frozen soil, as is typically confronted in arctic environments, requires substantially more energy, time and resources to move and manipulate. Also, the curing of concrete and other paving materials may be negatively impacted by such extreme cold temperature as required water evaporation and drying are particularly challenging when the liquid components freeze prior to evaporation.
These difficulties can be mitigated through the use of heaters to warm the work site area. One commonly used type of heater is a so-called indirect fired (IDF) heater that heats air and directs the hot-air to the area to be heated by blowing the air through large hoses. The air is heated by a burner that may be fueled by any of a variety of fuels including diesel fuel, kerosene, natural gas, or propane. Heaters that burn a liquid fuel, such as diesel fuel, typically use an atomizing burner supplied with the liquid fuel from a fuel tank via a pump. Atomizing burners operate by pressurizing a fuel oil and forcing it through a nozzle. The nozzle causes the fuel oil to atomize into fine droplets that are readily burned. The atomized fuel is exposed to an electric arc to begin the combustion reaction. When the reaction has stabilized, it is self-sustaining, and the electrode is no longer needed to maintain a flame. The fuel may be supplied in either a “one-pipe system”, in which a pump is sized to deliver only as much fuel to the burner as is needed at any given time, or a “two-pipe” system in which the pump delivers much more fuel than is typically required for combustion and the unused fuel is recycled back to the fuel tank. As much as 70-90% of the fuel pumped by a two-pipe system may be returned as unused fuel. Two-pipe systems typically are considered to be preferable to one-pipe systems because they are self-purging after an out-of-fuel condition. That is, air trapped in the fuel lines is automatically purged back to the tank as opposed to having to be manually bled from the fuel lines in a one-pipe system.
Most atomizing burners are designed for indoor use at near room temperature conditions. Several are designed to withstand temperatures now lower than 0° C., and no commercially available burner known to the inventors is capable of starting and operating at temperatures of −40° C. without some degree of modification to either the burner or the fuel supply. The limiting factor preventing operation below these temperatures is the fact that fuel viscosity increases as temperature decreases, resulting in the ejection of larger fuel droplets from the burner's nozzles at low temperatures. At low temperatures of on the order of −20° C. and lower, the larger atomized droplets are difficult to ignite and may not ignite at all. Even if ignition is established, the burner will run with excessive smoke because of ineffective precombustion mixing of the fuel and air.
After-market heaters are available for heating fuel as it is being ejected from the burner's nozzle, but such heaters are minimally effective, even for start up, at extremely low temperatures of on the order of −30° C. Even if these small heaters are effective at improving burner start-up, they are insufficient for maintaining a stable flame over prolonged use. Furthermore, installation of the after-market inline heater requires modification to the heater, and may compromise manufacturer warranties.
In addition, at extremely low temperatures, such fuel may form a solid wax precipitate which can clog both the fuel filter and the burner nozzle. Nozzle heaters are completely ineffective at preventing the formation of such a precipitate in a fuel filter.
Various tank-based or inline heaters have been proposed in an effort to alleviate these problems, but all such heaters have disadvantages. Some are supplied with energy with heat from the burner and, as such, are completely ineffective at start-up when the heater's components are at or near ambient temperature and heating is most critical. Other, electrically powered heaters, require so much energy to operate that they dramatically increase the electrical power draw of the heater.
Despite these prior attempts to design a heater for use in cold weather climates, there remains need for improvement. In light of the foregoing, a heater configured to recirculate and effectively pre-warm fuel is desired.